Communication device and communication method

ABSTRACT

There is provided a communication device capable of transmitting a transfer rate request signal while reducing it and reducing the interference and power consumption when the transfer rate request signal is transmitted substantially without lowering the transmission efficiency in the MIMO communication method. In this device, a modulation encoding unit ( 125 ) encodes and modulates transmission data transmitted to a communication partner of the MIMO communication method and the transfer rate request signal in the plurality of transmission antennas. A transmission unit ( 132 ) and a transmission antenna ( 134 ) transmit a signal from the modulation encoding unit ( 125 ). A transmission control unit ( 120 ) controls transmission of a signal transmitted from the transmission antenna ( 134 ) and transmits a transfer rate request signal of one transmission antenna via the transmission antenna ( 134 ) according to a comparison result between a difference of the transfer rate request signal in the respective transmission antenna of the communication partner and a predetermined value.

TECHNICAL FIELD

The present invention relates to a transmitting apparatus andtransmitting method of a MIMO (Multi-Input Multi-Output) communicationscheme that transmits different signals from a plurality of antennas.

BACKGROUND ART

In recent years, MIMO (Multi-Input/Multi-Output) communication attractsattention as a technique that enables communication of large amount ofdata such as image. In MIMO communication, different transmission data(substreams) is respectively transmitted from a plurality of antennas ofa transmitting side, and, on the receiving side, a plurality oftransmission data mixed together on a channel is demultiplexed to theoriginal transmission data using a channel estimation value.

In actuality, in MIMO communication, signals transmitted from atransmitting apparatus are received at the number of antennas largerthan or equal to the number of transmitting apparatuses, and the channelcharacteristics between the antennas are estimated based on pilotsignals inserted in the signals received at the antennas.

The estimated channel characteristics H is expressed by the matrix 2×2when there are two transmitting antennas and two receiving antennas, forexample. In MIMO communication, based on the inverse matrix of theobtained channel characteristics H and the received signals obtained atreceiving antennas, the transmission signals (substream) transmittedfrom transmitting antennas are obtained.

The principle of MIMO communication, when the number of antennas oftransmitter 10 and receiver 20 is two, respectively, will be describedusing FIG. 1A. Here, the signals transmitted from antennas 11 and 12 oftransmitter 10 are TX1 and TX2, respectively, and the signals receivedby antennas 21 and 22 of receiver 20 are RX1 and RX2, respectively. Atthis time, the received signals (RX1 and RX2) can be expressed byequation 1 shown in FIG. 1B.

Here, in equation 1, A indicates the channel characteristics betweentransmitting antenna 11 and receiving antenna 21, B indicates thechannel characteristics between transmitting antenna 12 and receivingantenna 21, C indicates the channel characteristics between transmittingantenna 11 and receiving antenna 22 and D indicates the channelcharacteristics between transmitting antenna 12 and receiving antenna22.

At this time, when only signal TX1 is transmitted to receiver 20, forexample, TX2 becomes an interference signal for receiver 20, and thesignal received by antenna 21 includes both the desired signal componentand interference signal component. The same holds true for antenna 22.

In order to remove (compensate) the above interference signal componentfrom the received signals and obtain the transmission signals (TX1 andTX2), it is necessary to obtain the inverse matrix of the matrix formedwith four channel characteristics A, B, C and D, as shown in equation 2.Therefore, transmitter 10 transmits a signal where a known signal (forexample, a pilot signal) for channel estimation is inserted in thetransmission signal, and receiver 20 performs channel estimation basedon this known signal, obtains channel characteristics A, B, C and D, andobtains the above inverse matrix.

In actuality, the steps for obtaining the transmission signals (TX1 andTX2) from the received signals (RX1 and RX2) include operations such asa ZF (Zero-Forcing) operation that demultiplexes substreams (each data)only through the inverse matrix operation expressed by equation 2 or anMMSE (Minimum Mean Square Error) operation that performs demultiplexingso as to minimize an error.

Thus, in MIMO communication, theoretically, a plurality of signalstransmitted at the same frequency and at the same time can berespectively demultiplexed at the receiver, thereby enabling high-speedand high-capacity communication.

By the way, in a MIMO communication scheme, a plurality of transmissionsystems that use radio sections provided with power amplifiers havinglarge power consumption are required on the transmitting side. It iswell known that, when a MIMO communication scheme is applied to uplink,the power consumption of receiver 20 will become extremely large.Further, downlink is considered important with respect to the throughputof a MIMO communication scheme. For these reasons, a MIMO communicationscheme is generally used only in downlink.

In such a MIMO communication scheme, as disclosed in Non-Patent Document1, to further improve the throughput, a method is studied ofindependently setting a transmission rate per antenna and transmitting aCQI (Channel Quality Indicator), which is a transmission rate settingsignal of each antenna.

A CQI is a signal that indicates the modulation scheme and coding rateof packet data that can be demodulated in receiver 20. Transmitter 10,such as a base station, for example, has the CQI transmitted fromreceiver 20 at a period set by an upper apparatus such as an RNC (RadioNetwork Controller). Transmitter 10 receiving the CQI performsscheduling using the CQI transmitted from receiver 20 and independentlyselects per antenna the optimum modulation scheme and coding rate. Then,transmitter 10 modulates and encodes the transmission data using theselected modulation scheme and coding rate, and transmits the data toreceiver 20 based on the scheduling result. By this means, by adaptivelychanging the transmission rate according to the radio wave propagationenvironment, it is possible to transmit large amount of data fromtransmitter 10 to receiver 20.

Non-Patent Document 1: 3GPP TR25.876

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

However, in a conventional MIMO communication scheme that independentlysets a transmission rate per antenna, the transmitter (transmittingapparatus) transmits to a communicating party the transmission raterequest signals (CQI) corresponding to the number of antennas, andtherefore the amount of transmission rate request signals transmittedfrom the receiver side to the transmitting side becomes equivalent timesof the number of antennas. Thus, when the transmission rate requestsignals are transmitted from the receiving side, there are problems thatinterference to other receivers (users) increases and receiver powerconsumption increases.

It is therefore an object of the present invention to provide acommunication apparatus and a communication method capable of reducingthe transmission rate request signals and performing transmissionwithout substantially reducing transmission efficiency, and reduceinterference and power consumption upon transmission of transmissionrate request signals.

Means for Solving the Problem

The communication apparatus of the present invention that transmitstransmission data and transmission rate request signals corresponding toa plurality of transmitting antennas to a communicating party of a MIMOcommunication scheme that transmits different data from the plurality oftransmitting antennas by independently setting a transmission rate pertransmitting antenna, employs a configuration including: a transmittingsection that transmits the transmission data and the transmission raterequest signals; and a controlling section that controls transmission ofsignals to be transmitted from the transmitting section, wherein thecontrolling section transmits, through the transmitting section, thetransmission rate request signals corresponding to less transmittingantennas than the plurality of transmitting antennas, based on acomparison result between a difference between the transmission raterequest signals of the transmitting antennas of the communicating partyand a predetermined value.

ADVANTAGEOUS EFFECT OF THE INVENTION

As described above, according to the present invention, in a MIMOcommunication scheme, it is possible to reduce the transmission raterequest signals and perform transmission without substantiallydecreasing transmission efficiency, and reduce interference and powerconsumption upon transmission of transmission rate request signals.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A illustrates the principle of MIMO communication when the numberof antennas of a transmitter and receiver is two, respectively;

FIG. 1B is an equation expressing the relationship between thetransmission signals and received signals of FIG. 1A;

FIG. 2 is a block diagram showing a configuration of a terminalapparatus, which is a communication apparatus, according to Embodiment 1of the present invention;

FIG. 3 is a block diagram showing a schematic configuration of atransmitting apparatus, which is one example of a communicating party ofthe terminal apparatus, shown in FIG. 2;

FIG. 4 is a flowchart showing a communication system having a terminalapparatus according to Embodiment 1 of the present invention;

FIG. 5 is a block diagram showing a configuration of a terminalapparatus, which is a communication apparatus, according to Embodiment 2of the present invention;

FIG. 6 is a block diagram showing a configuration of a terminalapparatus, which is a communication apparatus, according to Embodiment 3of the present invention;

FIG. 7 is a block diagram showing a configuration of a terminalapparatus, which is a communication apparatus, according to Embodiment 4of the present invention;

FIG. 8 is a flowchart showing a communication system having the terminalapparatus according to Embodiment 4 of the present invention; and

FIG. 9 is a block diagram showing a configuration of a terminalapparatus, which is a communication apparatus, according to Embodiment 5of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Now embodiments of the present invention will be described in detailwith reference to the drawings.

Embodiment 1

FIG. 2 is a block diagram showing the configuration of terminalapparatus 100, which is a communication apparatus, according toEmbodiment 1 of the present invention.

In a MIMO communication scheme, when the difference between thetransmission rate request signals of the transmitting antennas of acommunicating party is smaller than a predetermined value, bytransmitting only the transmission rate request signal corresponding toone antenna, terminal apparatus 100 of Embodiment 1 can reducetransmission rate request signals without substantially decreasingtransmission efficiency and reduce interference and power consumptionupon transmission of transmission rate request signals. Terminalapparatus 100 of the present embodiment using a CDMA (Code DivisionMultiple Access) communication scheme will be described.

Terminal apparatus (communication apparatus) 100 shown in FIG. 2 hastransmission controlling section 120 that controls transmission oftransmission data, modulating and encoding section 125 that modulatesand encodes the data to be transmitted, transmitting section 132 thatconverts the frequency to a radio frequency band, and transmittingantenna 134. Furthermore, terminal apparatus 100 has receiving antennas140 and 150, receiving sections 142 and 152, interference compensatingsection 160, transmission rate request generating sections 144 and 154,comparing section 163, P/S (parallel-to-serial) converting section(indicated by “P/S” in FIG. 2) 164, selecting section 165, decodingsection 166 and S/P (serial-to-parallel) converting section (indicatedby “S/P” in FIG. 2) 168. Transmission controlling section 120 controlstransmission of the transmission signal transmitted to transmittingapparatus (base station) 200, stores and outputs the transmission signalto modulating and encoding section 125 at the transmission time.

Further, transmission controlling section 120 controls transmissionbased on the transmission rate request signals of transmitting antennas210 and 220 of each communicating party inputted from transmission raterequest generating sections 144 and 154, and the retransmission requestsignal from S/P converting section 168.

Furthermore, transmission controlling section 120 controls transmissionof the transmission rate request signals based on the selection resultinputted from selecting section 165. To be more specific, transmissioncontrolling section 120 controls transmission of the transmission raterequest signals corresponding to the number of all antennas or thetransmission rate request signal corresponding to one transmittingantenna of the communicating party selected by selecting section 165.

Modulating and encoding section 125 modulates and encodes thetransmission data and outputs the result to transmitting section 132.The modulated and encoded transmission signal is converted to a radiofrequency band by transmitting section 132 and transmitted throughtransmitting antenna 134.

Receiving antennas 140 and 150 receive the data transmitted from acommunicating party (here, transmitting apparatus 200 shown in FIG. 3),and respectively output the data to corresponding receiving sections 142and 152.

Receiving sections 142 and 152 convert the frequency of the receivedsignals, which are radio frequency band signals received at receivingantennas 140 and 150, obtain baseband signals and output the signals tointerference compensating section 160.

Interference compensating section 160 performs interference compensationprocessing on the received signals converted to baseband signals,obtains the data transmitted from transmitting antennas of thecommunicating party, and outputs the obtained transmission data totransmission rate request generating sections 144 and 154 and P/Sconverting section 164.

Transmission rate request generating sections 144 and 154 performchannel quality estimation per antenna (for example, first and secondtransmitting antennas 210 and 220 shown in FIG. 3) of the communicatingparty, and generate a transmission rate request signal (CQI: ChannelQuality Indicator) of each antenna.

Transmission rate request generating sections 144 and 154 respectivelycorrespond to the transmitting antennas (for example, first and secondtransmitting antennas 210 and 220 shown in FIG. 3) of the communicatingparty, and outputs the quality estimation result including transmissionrate request signals of antennas.

As in the present embodiment, with the channel quality estimation methodperformed by transmission rate request generating sections 144 and 154,calculation can be performed based on four channel estimation results,when there are two receiving antennas of terminal apparatus 100 and twotransmitting antennas of transmitting apparatus 200 (refer to FIG. 3),which is the communicating party of terminal apparatus 100, describedlater. For example, quality information of first transmitting antenna210 (refer to FIG. 3) and second transmitting antenna 220 (refer to FIG.3) is calculated using channel estimation results A, B, C and D of thefour systems of FIG. 1. Quality information of first transmittingantenna 210 may be set to A+C, and quality information of secondtransmitting antenna 220 may be set to B+D. Furthermore, the qualityestimation method described here is only one example, the presentinvention is not limited to the quality estimation results describedhere and an arbitrary quality estimation method may be used.

Comparing section 163 calculates the difference between the qualityestimation results (to be more specific, a transmission rate signal ofeach transmitting antenna) inputted from transmission rate requestgenerating sections 144 and 154, compares the difference between thecalculated transmission rate request signal values of the antennas onthe transmitting side with a threshold value and outputs the result toselecting section 165. Here, the comparison result calculated bycomparing section 163 indicates whether or not to transmit thetransmission rate requests corresponding to the number of antennas ofthe communicating party that transmits data to terminal apparatus 100.

Based on the quality estimation results (including the transmission raterequest signal of each antenna) which are inputted from transmissionrate request generating sections 144 and 154 and respectively correspondto the antennas of the communicating party, and information inputtedfrom comparing section 163, selecting section 165 selects whether toinput to transmission controlling section 120 the transmission raterequest signals to be transmitted to the communicating partycorresponding to all antennas or corresponding to one antenna. Theselection result determined by selecting section 165 is outputted totransmission controlling section 120. Furthermore, when a retransmissionrequest signal is inputted from S/P converting section 168 totransmission controlling section 120, transmission controlling section120 transmits the retransmission request signal to the communicatingparty and transmits transmission rate request signals based on theselection result from selecting section 165.

P/S converting section 164 P/S converts the data obtained bycompensation by interference compensating section 160 and transmittedper transmitting antenna (for example, first and second transmittingantennas 210 and 220 shown in FIG. 3) of the communicating party, andoutputs the converted data to decoding section 166.

Decoding section 166 performs decoding processing on the data P/Sconverted by P/S converting section 164, and outputs the result to S/Pconverting section 168. Furthermore, when there is an error in thereceived signal, a retransmission request signal is extracted in S/Pconverting section 168 and outputted to transmission controlling section120. Upon reception of the retransmission request signal, transmissioncontrolling section 120 transmits the retransmission request signal tothe communicating party (here, transmitting apparatus 200 shown in FIG.3).

FIG. 3 is a block diagram showing a schematic configuration of atransmitting apparatus, which is one example of a communicating party ofterminal apparatus 100, according to Embodiment 1 of the presentinvention shown in FIG. 2.

Transmitting apparatus 200 shown in FIG. 3 is used, for example, as abase station and transmits different data from a plurality oftransmitting antennas (here, first transmitting antenna 210 and secondtransmitting antenna 220) to a plurality of terminal apparatuses.

Transmitting apparatus 200 has modulating and encoding sections 213 and223, transmitting sections 215 and 225, receiving antenna 240, receivingsection 243, demodulating section 245, decoding section 247, S/Pconverting section (indicated by “S/P” in FIG. 3) 249 and transmissioncontrolling section 260.

Transmission controlling section 260 controls transmission of thetransmission data (transmission signal). To be more specific,transmission controlling section 260 stores the transmission data andoutputs the data to modulating and encoding sections 213 and 223 at apredetermined transmission time.

Further, transmission controlling section 260 controls retransmissionbased on retransmission information transmitted from the communicatingparty (here, terminal apparatus 100), controls the transmission ratebased on transmission rate request signals transmitted from thecommunicating party and transmits transmission data using transmittingantennas based on the transmission rate request signals.

To be more specific, transmission controlling section 260 controlsretransmission based on the retransmission request signal (informationindicating that there is an error in the received signal) from S/Pconverting section 168. Then, when the transmission rate request signaltransmitted from the communicating party (here, terminal apparatus 100)corresponds to only one transmitting antenna, transmission controllingsection 260 controls the transmission rate so as to transmit data at thesame transmission rate at all transmitting antennas 210 and 220. In thiscase, modulating and encoding sections 213 and 223 select the samecoding rate and modulation scheme.

Modulating and encoding sections 213 and 223 perform encoding processingand modulating processing on the data to be transmitted—the data(indicated as “transmission signal” in FIG. 3) transmitted from firstand second transmitting antennas 210 and 220 of transmitting apparatus200—and output the result to transmitting sections 215 and 225.Furthermore, in modulation processing of modulating and encodingsections 213 and 223, normally the modulation scheme is setindependently per transmitting antennas 210 and 220 (3GPP TR25.876),however, when the transmission rate request signal from thecommunicating party (here, terminal apparatus 100) corresponds to onlyone antenna, the same coding rate and modulation scheme are set.

Transmitting sections 215 and 225 convert the frequency of the modulatedand encoded transmission data to a radio frequency band, and output theresult to first and second transmitting antennas 210 and 220. First andsecond transmitting antennas 210 and 220 transmit the frequencyconverted transmission data by transmitting sections 215 and 225.

Receiving antenna 240 receives and outputs the data transmitted from thecommunicating party to receiving section 243, and receiving section 243converts the frequency of the inputted received data to a basebandsignal and outputs the result to demodulating section 245.

Demodulating section 245 performs demodulating processing on theinputted received data after frequency conversion and outputs the resultto decoding section 247. Here, transmitting apparatus (base station) 200identifies whether the communicating party (terminal apparatus 100)transmits the transmission rate request signal corresponding to onetransmitting antenna or the transmission rate request signalscorresponding to a plurality of (here, two) transmitting antennas.

For example, in the present embodiment where a MIMO communication schemeis applied to the CDMA (Code Division Multiple Access) communicationscheme, demodulating section 245 compares the despreading results of thetransmission rate request signals of transmitting antennas 210 and 220,and determines that only the transmission rate request signalcorresponding to one transmitting antenna is transmitted when thedifference of the two is large.

In this way, even if terminal apparatus 100 does not necessarily reportinformation indicating corresponding to how many transmitting antennasthe transmission rate request signals are transmitted by thecommunicating party (terminal apparatus 100), transmitting apparatus 200can determine corresponding to how many transmitting antennas thetransmission rate request signals are transmitted by terminal apparatus100.

The received data, which is inputted from demodulating section 245 andconfigured in this way, is decoded by decoding section 247 and outputtedto S/P converting section 249.

S/P converting section 249 extracts the data, retransmission informationand transmission rate request information from the transmission signaltransmitted from the communicating party, and inputs the result totransmission controlling section 260. That is, S/P converting section249 sorts the received data (received signal) and the retransmissionrequest, quality information and information indicating the data to beretransmitted that are reported by the communicating party, and outputsthe result to transmission controlling section 260.

Next, the operation of a system having terminal apparatus 100 having theabove configuration, and transmitting apparatus 200 as a base stationwill be described using FIG. 4. FIG. 4 is a flowchart of a communicationsystem having communication apparatus (terminal apparatus) 100 accordingto Embodiment 1 of the present invention.

First, in step S1, terminal apparatus 100 receives a transmission signalfrom transmitting apparatus (base station) 200, which is a communicatingparty, through receiving antennas 140 and 150, and the flow proceeds tostep S2.

To be more specific, in step S1, in terminal apparatus 100, the receivedsignals received through receiving antennas 140 and 150 are converted tobaseband signals by receiving sections 142 and 152, subjected tointerference compensation processing by interference compensatingsection 160, and become data transmitted from each transmitting antennaof the communicating party.

In terminal apparatus 100, by using the transmission data frominterference compensating section 160, transmission rate requestgenerating sections 144 and 154 perform channel quality estimation perantenna (for example, first and second transmitting antennas 210 and 220shown in FIG. 3) of the communicating party, and generate a transmissionrate request signal of each antenna.

In step S2, terminal apparatus 100 determines whether or not thegenerated transmission rate request signal (transmission rate requestvalue) difference is smaller than a threshold value, the flow proceedsto step S3 when the difference is larger than or equal to the thresholdvalue, and the flow proceeds to step S4 when the difference is smallerthan the threshold value. To be more specific, in comparing section 163of terminal apparatus 100, the difference between the transmission raterequest values inputted from transmission rate request generatingsections 144 and 154 is calculated, the calculated transmission raterequest value difference and a threshold value are compared, and it isdetermined whether the calculated difference is larger or smaller thanthe threshold value (here, it is determined whether or not thedifference is smaller than the threshold value) is determined. Based onthis determination, comparing section 163 outputs to selecting section165 information indicating whether or not to transmit the transmissionrate requests corresponding to the number of antennas. The flow proceedsto step S3 when comparing section 163 outputs to selecting section 165information indicating that the transmission rate requests correspondingto the number of antennas are transmitted, and the flow proceeds to stepS4 when comparing section 163 outputs to selecting section 165information indicating that the transmission rate requests correspondingto the number of antennas are not transmitted.

In step S3, terminal apparatus 100 transmits the transmission raterequest values of all transmitting antennas of the communicating partyto the communicating party (transmitting apparatus 200), and the flowproceeds to step S5. To be more specific, in step S3, comparing section163 outputs information indicating whether or not to transmit thetransmission rate requests corresponding to the number of antennas toselecting section 165, and selecting section 165 selects informationindicating the transmission rate requests corresponding to the number ofantennas are transmitted from this information. Then, selecting section165 outputs the selected information and the transmission rate requestvalues inputted from transmission rate request generating sections 144and 154 to transmission controlling section 120. Through modulating andencoding section 125, transmitting section 132 and transmitting antenna134, transmission controlling section 120 transmits to transmittingapparatus 200 the transmission rate request values of all antennas(here, first and second transmitting antennas 210 and 220 shown in FIG.3) based on information from selecting section 165.

In step S4, terminal apparatus 100 compares the transmission raterequest values of the antennas (for example, first and secondtransmitting antennas 210 and 220) of the communicating party. To bemore specific, in step S4, the transmission rate request values of firsttransmitting antenna 210 and second transmitting antenna 220 arecompared, and it is determined whether or not quality of firsttransmitting antenna 210 is worse. The flow proceeds to step S6 whenquality of first transmitting antenna 210 is worse, and the flowproceeds to step S7 when quality of second transmitting antenna 220 isworse.

To be more specific, in step S4, information indicating that thetransmission rate requests corresponding to the number of antennas arenot transmitted is inputted from comparing section 163 to selectingsection 165 of terminal apparatus 100. Then, selecting section 165compares information inputted from transmission rate request generatingsections 144 and 154 (transmission rate request signal values of firstand second transmitting antennas 210 and 220 of the communicatingparty). Next, when quality of first transmitting antenna 210 is poor,selecting section 165 outputs the transmission rate request value offirst transmitting antenna 210 to transmission controlling section 120,and the flow proceeds to step S6. When quality of second transmittingantenna 200 is poor, selecting section 165 outputs the transmission raterequest value of second transmitting antenna 220 to transmissioncontrolling section 120, and the flow proceeds to step S7.

In step S6, in terminal apparatus 100, transmission controlling section120 transmits a retransmission request signal to transmitting apparatus200, which is the communicating party, transmits the transmission raterequest value of first transmitting antenna 210 of transmittingapparatus 200 based on the information from selecting section 165, andthen the flow proceeds to step S8.

In step S7, in terminal apparatus 100, transmission controlling section120 transmits to transmitting apparatus 200, which is the communicatingparty, the transmission rate request value of second transmittingantenna 220 of transmitting apparatus 200 based on information fromselecting section 165, and the flow proceeds to step S8.

After terminal apparatus 100 performs processing of the above steps S1to S3, S7 and S8, transmitting apparatus 200 receives through receivingantenna 240 the transmission signal including the transmission raterequest value transmitted from terminal apparatus 100 through thesesteps. Transmitting apparatus 200 that receives the transmission signalfrom terminal apparatus 100 obtains the transmission rate request valuesthrough receiving section 243, demodulating section 245, decodingsection 247 and S/P converting section 249, and performs processing ofsteps S5 and S8.

To be more specific, in step S5, upon reception of the transmission raterequest values of all transmitting antennas from terminal apparatus 100,transmitting apparatus 200 (refer to FIG. 3) independently sets thetransmission rate for each antenna (first and second transmittingantennas 210 and 220) and transmits data.

To be more specific, in step S5, transmission controlling section 260 oftransmitting apparatus 200 sets the transmission rates of transmittingantennas 210 and 220 and controls transmission of data based on thetransmission rate request obtained from the transmission signal ofterminal apparatus 100 through receiving antenna 240, receiving section243, demodulating section 245, decoding section 247 and S/P convertingsection 249. That is, based on the transmission rate request value fromterminal apparatus 100, transmission controlling section 260 transmitsthe same data from first and second transmitting antennas 210 and 220through modulating and encoding sections 213 and 223, and transmittingsections 215 and 225.

Further, in step S8, transmitting apparatus 200 sets, as thetransmission rate of all transmitting antennas, the transmission raterequest value from terminal apparatus 100 obtained through receivingantenna 240, receiving section 243, demodulating section 245, decodingsection 247 and S/P converting section 249, and transmits thetransmission data at the same transmission rate.

Thus, terminal apparatus 100 according to the present inventiontransmits the transmission rate request signals corresponding to allantennas of the communicating party (transmitting apparatus 200) whenthe difference between the transmission rate request values (CQI values)for the communicating party (transmitting apparatus 200) is larger thana threshold value. The communicating party (transmitting apparatus 200)receiving the transmission rate request signal independently sets thetransmission rate per antenna (here, first and second transmittingantennas 210 and 220) and performs transmission.

On the other hand, when the difference between the transmission raterequest values (CQI values) for the communicating party (transmittingapparatus 200) is smaller than a threshold value, terminal apparatus 100transmits the transmission rate request signals corresponding to thenumber of antennas less than the total number of antennas of thecommunicating party (transmitting apparatus 200). The communicatingparty (transmitting apparatus 200) receiving the transmission raterequest signal sets the transmission rate based on the transmission raterequest signal from terminal apparatus 100 as the same transmission ratefor all antennas, and transmits transmission data from all antennas.

To be more specific, when it is determined that the difference betweentransmission rate requests is smaller than a threshold value and qualityof first transmitting antenna 210 is worse, terminal apparatus 100transmits the transmission rate request signal of first transmittingantenna 210 to transmitting apparatus 200, which is the communicatingparty, and transmitting apparatus 200 sets the reported transmissionrate request value of first transmitting antenna 210 as the sametransmission rate for all antennas and transmits the transmission data.

Further, when it is determined that the difference between transmissionrate requests is smaller than a threshold value and quality of secondtransmitting antenna 220 is worse, terminal apparatus 100 transmits thetransmission rate request signal of second transmitting antenna 220 totransmitting apparatus 200, which is the communicating party, andtransmitting apparatus 200 sets the reported transmission rate requestvalue of second transmitting antenna 220 as the same transmission ratefor all antennas and transmits the transmission data.

Furthermore, when the difference between the transmission rate requestvalue of each transmitting antenna of the communicating party calculatedby terminal apparatus 100 is smaller than a threshold value, in theabove description, to prevent a decrease in the error rate, out oftransmission antennas provided with the communicating party, atransmission rate request signal having the worst quality istransmitted.

Thus, according to the present embodiment, when the difference betweenthe transmission rate request values of transmitting antennas 210 and220 of transmitting apparatus 200 is smaller than a threshold value, thetransmission rate request values transmitted from terminal apparatus 100corresponding to all transmission antennas of transmitting apparatus 200are not transmitted, and the transmission rate request valuecorresponding to only one antenna is transmitted. Upon reception of thetransmission rate request value, transmitting apparatus 200 performscommunication using the same transmission rate for all antennas. Thus,terminal apparatus 100 can reduce the transmission rate request signalswithout substantially decreasing transmission efficiency and reduceinterference and power consumption. Further, transmitting apparatus 200can reduce the amount of control information of downlink withoutsubstantially decreasing the throughput.

For example, in a communication scheme that adaptively changes thetransmission rate, regardless of a MIMO communication scheme, it isnecessary to transmit, to the communicating party, informationindicating at which transmission rate data is transmitted.

Particularly, in a MIMO communication scheme that sets transmissionrates per antenna, when information indicating at which transmissionrate data is transmitted is transmitted to a transmitting apparatus,information and the amount of control signals of downlink becomeequivalent times of the number of antennas.

Conversely, in the present embodiment, when transmitting apparatus 200performs communication at the same transmission rate for alltransmitting antennas, only control information corresponding to oneantenna needs to be transmitted from terminal apparatus 100, which isthe communicating party of transmitting apparatus 200, thereby reducingthe amount of control information of downlink without substantiallydecreasing the throughput.

Furthermore, although the case has been described in the presentembodiment where the number of transmitting antennas of transmittingapparatus 200, which is the communicating party of terminal apparatus100, is two, the number of transmitting antennas of the transmittingapparatus is not limited to this and may be arbitrarily set.

Furthermore, in contrast to the present embodiment, a method oftransmitting the transmission rate request signal of the transmittingantenna having the best quality is also possible. To improve thecapacity of the overall system, it is better to transmit thetransmission rate request signal of the transmitting antenna having thebest quality. An example of the above method will be described inEmbodiment 4. Also, a method of changing the transmission rate signal tobe transmitted between upon first transmission and upon retransmissionis also possible (upon first transmission, the transmission rate requestsignal of the antenna having the best quality is transmitted, and uponretransmission, the transmission rate request signal of the antennahaving the worst quality is transmitted).

Embodiment 2

FIG. 5 is a block diagram showing the configuration of terminalapparatus 300, which is a communication apparatus, according toEmbodiment 2 of the present invention.

Terminal apparatus 300 of Embodiment 2 can further reduce falsedetection of transmission rate request signals by the communicatingparty than terminal apparatus 100 of Embodiment 1 by transmitting to acommunicating party information indicating whether the transmission raterequest signals corresponding to the number of transmitting antennas ofthe communicating party are transmitted or the transmission rate requestsignal corresponding to only one antenna is transmitted.

First, the transmitting apparatus, such as a base station, which is acommunicating party of terminal apparatus 300 of Embodiment 2 will bedescribed.

The transmitting apparatus, which is a communicating party of terminalapparatus 300 of Embodiment 2 has the same configuration with slightdifference in operation, compared to transmitting apparatus 200 ofEmbodiment 1 (refer to FIG. 3). Thus, only the different operation willbe described, and the operations of other components will be omitted.

The operation of the transmitting apparatus, which is a communicatingparty of terminal apparatus 300 of Embodiment 2, differs from that oftransmitting apparatus 200 of FIG. 3 in the operation of S/P convertingsection 249. That is, in the transmitting apparatus of Embodiment 2,when transmitting apparatus 200 of FIG. 3 is referred to, S/P convertingsection 249 outputs a retransmission request signal (informationindicating whether or not there is an error in the received signal) totransmission controlling section 320, and, based on information which isreported by terminal apparatus 300 and indicates corresponding to howmany antennas the transmission rate request signals are transmitted,extracts and outputs the transmission rate request signals totransmission controlling section 260.

Further, the transmitting apparatus of Embodiment 2, similar totransmitting apparatus 200 of Embodiment 1, is used as, a base station,or the like of a MIMO communication scheme applied to a CDMAcommunication scheme, and can identify whether terminal apparatus 300transmits the transmission rate request signal corresponding to oneantenna or the transmission rate request signals corresponding to aplurality of (here, two) antennas. For identification at thetransmitting apparatus, a method is used of, for example, comparing theresults of despreading the transmission rate request signals oftransmitting antennas and determining that the transmission rate requestsignal corresponding to only one antenna is transmitted when thedifference between the two is large.

In this way, even if terminal apparatus 300 does not necessarily reportinformation indicating corresponding to how many transmitting antennasthe transmission rate request signals are transmitted by terminalapparatus 300, the base station can determine the transmission raterequest signals corresponding to how many antennas are transmitted bythe terminal. However, to reduce false detection of transmission raterequest signals by the transmitting apparatus, the method is effectiveof transmitting to the transmitting apparatus information indicatingcorresponding to how many antennas the transmission rate request signalsare transmitted by terminal apparatus 300.

Here, information indicating corresponding to how many antennas thetransmission rate request signals are transmitted by terminal apparatus300 may be one bit if there are two antennas, for example, and issufficiently small compared to a transmission rate request signal (forexample, the transmission rate request signal in 3GPP requires 5 bits),so that the amount of uplink control information does not substantiallyincrease.

Terminal apparatus 300 shown in FIG. 5 has the configuration thatremoves selecting section 165 from a configuration of terminal apparatus100 of Embodiment 1 (refer to FIG. 2), and basically has the sameconfiguration. Thus, in terminal apparatus 300 of the presentembodiment, different components from terminal apparatus 100 (refer toFIG. 2) will be described, and other same components will be assignedthe same reference numerals without further explanations.

In terminal apparatus 300 shown in FIG. 5, transmission rate requestgenerating sections 144 and 154 output the quality estimation resultsrespectively corresponding to the antennas of the communicating party(including the transmission rate request signal of each transmittingantenna) to comparing section 163 and transmission controlling section320. Furthermore, the channel quality estimation method used bytransmission rate request generating sections 144 and 154 is the same asdescribed in Embodiment 1, and therefore description thereof will beomitted.

Comparing section 163 calculates the difference between the qualityestimation results (to be more specific, transmission rate signals ofthe transmitting antennas) inputted from transmission rate requestgenerating sections 144 and 154, compares the transmission rate requestsignal value of each antenna on the transmitting side with a thresholdvalue, and outputs the result to transmission controlling section 320.Here, the comparison result calculated by comparing section 163indicates corresponding to how many transmission antennas of thecommunicating party, the transmission rate request signals to betransmitted to the communicating party that transmits data to terminalapparatus 300 are transmitted.

Transmission controlling section 320 controls transmission of thetransmission signal transmitted to the communicating party (for example,transmitting apparatus 200) and, similar to transmission controllingsection 120, stores and outputs the transmission signal to modulatingand encoding section 125 at the transmission time.

Further, transmission controlling section 320 controls transmissionbased on the transmission rate request signals of the transmittingantennas (for example, per first and second transmitting antennas 210and 220) of the communicating party, which are inputted fromtransmission rate request generating sections 144 and 154 andinformation which is inputted from comparing section 163 and indicateswhether or not the transmission rate requests corresponding to thenumber of antennas are transmitted. To be more specific, transmissioncontrolling section 320 controls transmission of information which isinputted from comparing section 163 and indicates whether or not thetransmission rate requests corresponding to the number of antennas aretransmitted, and the transmission of transmission rate request signalsof the transmitting antennas corresponding to this information, to thetransmitting apparatus, which is the communicating party.

Thus, in Embodiment 2, terminal apparatus 300 transmits to thecommunicating party information indicating whether or not thetransmission rate requests corresponding to the number of antennas aretransmitted. As a result, it is possible to further reduce falsedetection of transmission rate request signals, compared to a case whereterminal apparatus 100 of Embodiment 1 is used.

Furthermore, in transmitting apparatus (base station) 200 (refer to FIG.3) receiving a signal from terminal apparatus 300, S/P convertingsection 249 extracts the retransmission request signal and transmissionrate request signals based on information which is reported by terminalapparatus 300 and indicates corresponding to how many antennas thetransmission rate request signals are transmitted, and outputs theextraction result to transmission controlling section 260 (refer to FIG.3). The transmission rates based on this information are set forpredetermined transmitting antennas, and data transmission is performedfrom the transmitting antennas.

Embodiment 3

FIG. 6 is a block diagram showing the configuration of terminalapparatus 400, which is a communication apparatus, according toEmbodiment 3 of the present invention.

Terminal apparatus 400 of Embodiment 3, has a variable threshold valueused to select whether the transmission rate request signalscorresponding to the number of transmitting antennas of thecommunicating party are transmitted or the transmission rate requestsignal corresponding to one antenna is transmitted, in comparing section163 of transmitting apparatus 300 of Embodiment 2.

As shown in FIG. 6, terminal apparatus 400 has a configuration where thethreshold value inputted to comparing section 163 of terminal apparatus300 (refer to FIG. 5) is selected by selecting section 465. Terminalapparatus 400 has a configuration that further adds selecting section465 in the configuration of terminal apparatus 300 corresponding toEmbodiment 2 shown in FIG. 5, and other configuration is basically thesame as terminal apparatus 300. Thus, the same components will beassigned the same reference numerals without further explanations.

In terminal apparatus 400, comparing section 163 receives from selectingsection 465 as input a threshold value for comparing the differencebetween the quality estimation results (to be more specific,transmission rate signals of the transmitting antennas) inputted fromtransmission rate request generating sections 144 and 154, and athreshold value.

Selecting section 465 receives a predetermined number of thresholdvalues as input. Selecting section 465 selects a predetermined thresholdvalue from the inputted predetermined number of threshold values andoutputs the selection result to comparing section 163.

In Embodiment 3, the threshold values of the selection targets inselecting section 465 are two threshold values “threshold value 1” and“threshold value 2.” Furthermore, although a case of two thresholdvalues has been described in the present embodiment, the presentinvention is not limited to this, and an arbitrary number of thresholdvalues may be used. In this case as well, the comparison resultcalculated by comparing section 163 is outputted to transmissioncontrolling section 420, and indicates whether or not to transmit thetransmission rate requests to be transmitted to the communicating partythat transmits data to terminal apparatus 400 corresponding to thenumber of antennas of the communicating party.

The other components of terminal apparatus 400 and advantages obtainedby the other components are the same as terminal apparatus 300 ofEmbodiment 2, and description thereof will be omitted.

Furthermore, in selecting section 465, the optimum value of thethreshold value used for selecting corresponding to how manytransmission antennas the transmission rate request signals aretransmitted to the transmitting apparatus of a base station, which isthe communicating party, is changed according to various communicationconditions. For example, in the following case, threshold values areset, and selecting section 465 selects and outputs a threshold value tocomparing section 163.

1) Selecting a Threshold Value According to the Number of Users Usingthe Channel

When there are a large number of users, it is necessary to reduceinterference to other users, and therefore a large threshold value isset, and, preferably a transmission rate request signal corresponding toonly one antenna is transmitted.

2) Selecting a Threshold Value According to Battery Power of a Terminal

When there is low battery power, it is necessary to reduce powerconsumption, and therefore a large threshold value is set, and,preferably a transmission rate request signal corresponding to only oneantenna is transmitted.

Furthermore, the threshold value selection method of terminal apparatus400 of Embodiment 3 is only one example, the present invention is notlimited to this, and each threshold value may be changed based onarbitrary conditions.

Embodiment 4

FIG. 7 is a block diagram showing the configuration of terminalapparatus 500, which is a communication apparatus, according toEmbodiment 4 of the present invention.

Terminal apparatus 500 of Embodiment 4 has basically the sameconfiguration as terminal apparatus 100 corresponding to Embodiment 1shown in FIG. 2, and the same components will be assigned the samereference numerals without further explanation. To be more specific, interminal apparatus 500, compared to terminal apparatus 100 (refer toFIG. 2), the advantages of transmission controlling section 520,selecting section 565 and comparing section 563 are different, and theadvantages of other components are almost the same. Furthermore, thecommunicating party of terminal apparatus 500 has the same basicconfiguration as transmitting apparatus 200 (refer to FIG. 3). Thus,only the difference of the transmitting apparatus according to thepresent embodiment will be described, and the same configuration will beomitted.

In terminal apparatus 500 shown in FIG. 7, a transmission signal isfirst stored in transmission controlling section 520 and then inputtedto modulating and encoding section 125 at the transmission time. Here,transmission controlling section 520 controls transmission of thetransmission rate request signals and retransmission request signalsbased on the selection result of whether the transmission rate requestsignals, which are inputted from selecting section 565, are inputted tothe transmission controlling section, corresponding to all antennas orcorresponding to one antenna.

Next, modulating and encoding section 125 performs modulating andencoding processing on the transmission data inputted from transmissioncontrolling section 520 and outputs the result to transmitting section132. Transmitting section 132 converts to a radio frequency band thefrequency of the transmission signal subjected to modulating andencoding processing, outputs the converted signal to transmittingantenna 134 and transmits the result to the communicating party throughtransmitting antenna 134.

When terminal apparatus 500 receives transmission data from thecommunicating party (for example, a base station having theconfiguration of transmitting apparatus 200 shown in FIG. 3), terminalapparatus 500 performs the following operation.

The data transmitted from the base station is received by receivingantennas 140 and 150, and converted to a baseband signal by receivingsections 142 and 152. The transmission data converted to a basebandsignal is outputted to interference compensating section 160 andsubjected to interference compensation by interference compensatingsection 160. Thus, interference compensating section 160 obtains thedata transmitted per transmitting antenna of the communicating party.Then, the data outputted from interference compensating section 160 isoutputted to P/S converting section 164, is subjected to P/S conversion,is outputted to transmission rate request generating sections 144 and154 and is subjected to quality estimation per transmitting antenna ofthe base station, and quality estimation results including thetransmission rate request signal of each transmitting antenna arecalculated.

The P/S converted data in P/S converting section 164 is subjected todecoding processing by decoding section 166. In decoding section 166,when there is an error in the received signal, data including aretransmission request signal is outputted to S/P converting section168. Furthermore, the retransmission request signal is extracted by S/Pconverting section 168 and inputted to transmission controlling section520.

On the other hand, quality estimation is performed per transmittingantenna of the communicating party by transmission rate requestgenerating sections 144 and 154, and the estimation results areoutputted to selecting section 565. Further, the quality estimationresults by transmission rate request generating sections 144 and 154 areoutputted to comparing section 563 and compared. The comparison resultcalculated in comparing section 563 is outputted to selecting section565 as information indicating from which antenna the communicating partyperforms transmission. Then, selecting section 565 selects, based on theinput information, whether to input the transmission rate requestsignals to transmission controlling section 520 corresponding to allantennas or corresponding to one antenna having good quality.

Now, the configuration of the communicating party of terminal apparatus500 of Embodiment 4 will be described.

The base station, which is the communicating party of terminal apparatus500 of Embodiment 4, has the same configuration as transmittingapparatus 200 (refer to FIG. 3). Thus, the base station, which is thecommunicating party of terminal apparatus 500 of Embodiment 4, will nowbe described with reference to FIG. 3.

In the base station of the present embodiment, when, in theconfiguration shown in FIG. 3, transmission controlling section 260receives the transmission rate request signal, which is transmitted fromthe terminal, corresponding to only one transmitting antenna,transmission controlling section 260 controls the transmission rates oftransmitting antennas 210 and 220 so as to perform transmission usingthe same transmission rate. In this case, modulating and encodingsections 213 and 223 select the same coding rate and modulation scheme.Further, transmission controlling section 260 also controlsretransmission when a retransmission request signal is reported byterminal apparatus 500 (refer to FIG. 7). Then, the transmission data issubjected to modulating and encoding processing by modulating andencoding sections 213 and 223.

Furthermore, although modulating and encoding sections 213 and 223independently set the coding rate and modulation scheme per transmittingantennas 210 and 220 (3GPP TR25,876), modulating and encoding sections213 and 223 select the same coding rate and modulation scheme when thetransmission rate request signal, which is transmitted from terminalapparatus 500, corresponds to one transmitting antenna only. Then, thefrequency of the encoded and modulated transmission signal is convertedto a radio frequency band by transmitting sections 215 and 225, andtransmitted through transmitting antennas 210 and 220. Here, when thequality (channel quality) difference between transmitting antennas 210and 220 is large and terminal apparatus 500 transmits the transmissionrate request signal corresponding to only one antenna, data istransmitted only from the transmitting antenna having good quality, andno data is transmitted from the other transmitting antenna having poorquality.

Here, when the base station performs transmission only from one antennahaving good quality, methods of selecting from which antennatransmission is performed, may include, for example, using thetransmission rate request signals, which are transmitted from theterminal upon previous transmission corresponding to all antennas andselecting from which antenna transmission is performed. That is, in theprevious transmission rate request signals, when first transmittingantenna 210 has a larger transmission rate request value, transmissionis performed from only first transmitting antenna 210, and when secondtransmitting antenna 220 has a larger transmission rate request value,transmission is performed from only second transmitting antenna 220.However, the selection method is not limited to this.

Next, FIG. 8 illustrates operation of a system having terminal apparatus500 will be described. FIG. 8 is a flowchart of a communication systemhaving communication apparatus (terminal apparatus) 500 according toEmbodiment 4 of the present invention.

First, in step S21, terminal apparatus 500 (refer to FIG. 7) receivestransmission signals from a base station, which is a communicatingparty, through receiving antennas 140 and 150, and the flow proceeds tostep S22.

To be more specific, in step S21, in terminal apparatus 500, thereceived signals received through receiving antennas 140 and 150 areconverted to baseband signals by receiving sections 142 and 152,subjected to interference compensation processing by interferencecompensating section 160 and transmitted from the transmitting antennasof the communicating party.

In terminal apparatus 500, by using the transmission data frominterference compensating section 160, transmission rate requestgenerating sections 144 and 154 perform channel quality estimation perantenna (for example, per first and second transmitting antennas 210 and220 shown in FIG. 3) of the communicating party, and generate atransmission rate request signal of each antenna.

In step S22, terminal apparatus 500 determines whether or not thedifference of the generated transmission rate request signals(transmission rate request value) is larger than a threshold value. Theflow proceeds to step S23 when the difference is equal to or smallerthan the threshold value, and the flow proceeds to step S24 when thedifference is larger than the threshold value.

To be more specific, comparing section 563 of terminal apparatus 500calculates the difference between the transmission rate request valuesinputted from transmission rate request generating sections 144 and 154,compares the difference of the calculated transmission rate requestvalue with a threshold value and determines whether the difference islarger or smaller than the threshold value (here, whether or not thedifference is larger than the threshold value). Based on thisdetermination, comparing section 563 outputs to selecting section 565information indicating from which antenna the communicating partyperforms transmission. Comparing section 563 proceeds to step S23 orstep S24 based on information outputted to selecting section 565.

In step S23, terminal apparatus 500 transmits the transmission raterequest values of all transmitting antennas of the communicating partyto the communicating party (for example, transmitting apparatus 200),and the flow proceeds to step S25.

To be more specific, in step S23, information inputted from comparingsection 563 is transmitted from all antennas of the communicating party,and outputted to selecting section 565. Based on information indicatingthat the transmission rate requests corresponding to all antennas aretransmitted, selecting section 565 selects all transmission rate requestvalues inputted from transmission rate request generating sections 144and 154, and outputs the selection result to transmission controllingsection 520. Through modulating and encoding section 125, transmittingsection 132 and transmitting antenna 134, transmission controllingsection 520 transmits to transmitting apparatus 200 the transmissionrate request values of all antennas (here, first and second transmittingantennas 210 and 220 shown in FIG. 3) based on the information fromselecting section 565, and the flow proceeds to step S25.

On the other hand, in step S24, terminal apparatus 500 compares thetransmission rate request values of the antenna (for example, first andsecond transmitting antennas 210 and 220) of the communicating party. Tobe more specific, in step S24, comparing section 563 compares thetransmission rate request values of first transmitting antenna 210 andsecond transmitting antenna 220 and determines whether or not quality offirst transmitting antenna 210 is better. The flow proceeds to step S26when quality of first transmitting antenna 210 is better, and the flowproceeds to step S27 when quality of second transmitting antenna 220 isbetter.

To be more specific, in step S24, selecting section 565 of terminalapparatus 500 receives as input from comparing section 563 informationindicating from which antenna the communicating party performstransmission, that is, information indicating an antenna having the bestquality. Then, based on information from comparing section 563,selecting section 565 selects information inputted from transmissionrate request generating sections 144 and 154 (the transmission raterequest signal values of first and second transmitting antennas 210 and220 of the communicating party), and outputs the selection result totransmission controlling section 520.

To be more specific, selecting section 565 outputs the transmission raterequest value of first transmitting antenna 210 to transmissioncontrolling section 520 when quality of first transmitting antenna 210is good, and the flow proceeds to step S26. Selecting section 565outputs the transmission rate request value of second transmittingantenna 210 to transmission controlling section 520 when quality ofsecond transmitting antenna 220 is good, and the flow proceeds to stepS27.

In step S26, in terminal apparatus 500, transmission controlling section520 transmits to the base station, which is the communicating party (tobe more specific, transmitting apparatus 200), the transmission raterequest value of first transmitting antenna 210 of transmittingapparatus 200 based on information from selecting section 565, and theflow proceeds to step S28.

In step S27, in terminal apparatus 500, transmission controlling section520 transmits to the base station which is the communicating party(here, transmitting apparatus 200), the transmission rate request valueof a predetermined antenna (here, second transmitting antenna 220) ofthe base station (transmitting apparatus 200) based on information fromselecting section 565, and the flow proceeds to step S28.

After processing of the above steps S21 to S23, S27 and S28 in terminalapparatus 500, the transmission signal that is transmitted from terminalapparatus 500 through these steps and includes the transmission raterequest values is received by the base station and is subjected toprocessing of step S25 and step S28. When the base station has the sameconfiguration as transmitting apparatus 200 (refer to FIG. 3), the basestation (transmitting apparatus 200) receives the transmission signalfrom terminal apparatus 500 through receiving antenna 240. Then, throughreceiving section 243, demodulating section 245, decoding section 247and S/P converting section 249, the base station obtains thetransmission rate request values, and the processing of step S25 andstep S28 is performed.

That is, in step S25, upon reception of the transmission rate requestvalues of all transmitting antennas from terminal apparatus 500, thebase station (transmitting apparatus 200 shown in FIG. 3) independentlysets the transmission rate for the antennas (first and secondtransmitting antennas 210 and 220) and transmits the same data.Furthermore, processing in step S25 is the same as step S5 shown in FIG.4, and detailed description thereof will be omitted.

Further, in step S28, the base station having the same configuration astransmitting apparatus 200 shown in FIG. 3 sets as the transmission rateof all transmitting antennas the transmission rate request value fromterminal apparatus 500 obtained through receiving antenna 240, receivingsection 243, demodulating section 245, decoding section 247 and S/Pconverting section 249, and transmits transmission data at the sametransmission rate. That is, in step S28, the base station performstransmission only from the transmitting antenna having good qualitycorresponding to the transmission rate request value transmitted fromterminal apparatus 500.

Thus, in terminal apparatus 500 according to the present invention, whenthe difference between the transmission rate request values (CQI values)for the communicating party (transmitting apparatus 200) is equal to orsmaller than a threshold value, the transmission rate request signals ofall antennas of the communicating party (transmitting apparatus 200) aretransmitted. The communicating party (transmitting apparatus 200)receiving the transmission rate request signals independently sets thetransmission rate per antenna (here, first and second transmittingantennas 210 and 220), and performs transmission.

On the other hand, in terminal apparatus 500, when the differencebetween the transmission rate request values (CQI values) for thecommunicating party (transmitting apparatus 200) is larger than athreshold value, the transmission rate request signals corresponding toless antennas than the total number of antennas of the communicatingparty (transmitting apparatus 200) are transmitted. The communicatingparty (transmitting apparatus 200) receiving the transmission raterequest signals sets a transmission rate based on the transmission raterequest signals from terminal apparatus 500 for the requested number oftransmitting antennas, and transmits transmission data. Further, thecommunicating party sets the transmission rate corresponding to thetransmitted transmission rate request value as the same transmissionrate for all antennas, and transmits transmission data from allantennas.

To be more specific, in terminal apparatus 500, when it is determinedthat the difference between transmission rate requests is larger than athreshold value and quality of first transmitting antenna 210 is better,terminal apparatus 500 transmits the transmission rate request signal offirst transmitting antenna 210 to transmitting apparatus 200, which isthe communicating party. Transmitting apparatus 200 sets the reportedtransmission rate request value of first transmitting antenna 210 forrequested first transmitting antenna 210 and transmits transmissiondata. Further, the communicating party sets the transmitted transmissionrate request value as the same transmission rate for all antennas, andtransmits transmission data from all antennas.

Further, in terminal apparatus 500, when it is determined that thedifference between transmission rate requests is larger than a thresholdvalue and quality of second transmitting antenna 220 is better, terminalapparatus 500 transmits the transmission rate request signal of secondtransmitting antenna 220 to transmitting apparatus 200, whish is thecommunicating party. Transmitting apparatus 200 sets the reportedtransmission rate request value of second transmitting antenna 220 forsecond transmitting antenna 220, and transmits transmission data.Further, the communicating party sets the transmission ratecorresponding to the transmitted transmission rate request value as thesame transmission rate for all antennas, and transmits transmission datafrom all antennas.

When the difference between the transmission rate request signals of thetransmitting antennas of the communicating party (for example,transmitting apparatus 200 shown in FIG. 3) is larger than apredetermined value, terminal apparatus 500 transmits only thetransmission rate request signal corresponding to one antenna, so thatit is possible to reduce the amount of transmission rate request signalswithout substantially decreasing uplink transmission efficiency andreduce interference and power consumption.

Thus, terminal apparatus 500 has a communicating party having the sameconfiguration as terminal apparatus 100—a plurality of transmittingantennas—, and receives transmission signals from the communicatingparty of a MIMO communication scheme where a transmission rate is setper transmitting antenna. When transmission rate request value of eachtransmission antenna receiving and extracting signals in this way islarge, the transmission rate request signal corresponding to one antennais transmitted, and the communicating party performs transmission onlyfrom an antenna having good quality. As a result, it is possible toreduce the amount of transmission rate request signals withoutsubstantially decreasing throughput.

That is, in a communication scheme that adaptively changes thetransmission rate, regardless of a MIMO communication scheme,information indicating at which transmission rate transmission isperformed needs to be transmitted to the communicating party.

Particularly, in a MIMO communication scheme that sets a transmissionrate per antenna, when information indicating at which transmission ratetransmission is performed is transmitted to the transmitting apparatus,information and the amount of control signals in downlink becomeequivalent times of the number of antennas. In contrast to this, in thepresent embodiment, when transmitting apparatus 200 performscommunication using the same transmission rate at all transmittingantennas, only the control information corresponding to one antennaneeds to be transmitted from terminal apparatus 500, which is thecommunicating party of transmitting apparatus 200, so that it ispossible to reduce the amount of control information in downlink withoutsubstantially decreasing the throughput.

In general, when the difference between transmission rate request valuesof the transmitting antennas receiving and extracting signals from abase station is large, the data transmission amount that can betransmitted from the transmitting antenna of the communicating partyhaving the worst quality is much less than the data transmission amountthat can be transmitted from a transmitting antenna having good quality.In such a case, the throughput does not substantially improve even ifthe transmission rate is set independently per antenna and thetransmission rate request signals corresponding to all antennas aretransmitted to the base station. Conversely, by transmitting thetransmission rate request signals corresponding to all transmittingantennas to the communicating party, the amount of transmission raterequest signals becomes equivalent times of the number of antennas,thereby increasing interference and power consumption. For this reason,when the difference between the transmission rate request values pertransmitting antenna is large, even if the transmission rate requestsignals corresponding to all antennas are transmitted to the basestation, the advantage becomes small, and the problem becomessubstantial. The present embodiment improves this problem.

Furthermore, although the case has been described in the presentembodiment where the number of transmitting antennas of transmittingapparatus 200, which is the communicating party of terminal apparatus500, is two, the present invention is not limited to this, and thenumber of transmitting antennas of the transmitting apparatus may bearbitrarily set.

Furthermore, in the present embodiment, when the communicating party(for example, a base station) of terminal apparatus 500 performstransmission only from one antenna having good quality, methods ofselecting from which antenna transmission is performed include, forexample, selecting from which antenna transmission is performed usingthe transmission rate request signals corresponding to all antennastransmitted from the terminal upon previous transmission. That is, inthe previous transmission rate request signals, transmission isperformed only from first transmitting antenna 210 when firsttransmitting antenna 210 has a larger transmission rate request value,and transmission is performed only from second transmitting antenna 220when second transmitting antenna 220 has a larger transmission raterequest value.

Thus, even if terminal apparatus 500 does not necessarily reports to thebase station information indicating whether or not a signal indicating atransmitting antenna is transmitted, the base station can select fromwhich antenna transmission is performed. However, in a communicationsystem having above terminal apparatus 500 and the above transmittingapparatus, when terminal apparatus is moving fast, the channel stateupon report of the previous transmission rate request values may greatlydiffer from the channel state upon transmission at the base station (thecommunicating party of terminal apparatus 500).

When a signal is transmitted from the base station under suchcircumstances, it is not likely to perform transmission from thetransmitting antenna having the best quality, and the throughputdecreases.

To prevent a decrease in the throughput under such circumstances, amethod is effective of transmitting a signal including informationindicating the transmitting antenna from the terminal apparatus, andselecting the transmitting antenna using the information indicating thetransmitting antenna at the base station. A terminal apparatus capableof realizing such a method is described in Embodiment 5.

Embodiment 5

FIG. 9 is a block diagram showing the configuration of terminalapparatus 600, which is a communication apparatus, according toEmbodiment 5 of the present invention.

By transmitting to the communicating party information indicating thetransmitting antenna of the communicating party, terminal apparatus 600can further prevent a decrease in the throughput particularly duringhigh-speed movement compared to Embodiment 4.

Terminal apparatus 600 shown in FIG. 9 has a configuration that removesselecting section 565 from a configuration of terminal apparatus 500 ofEmbodiment 4 (refer to FIG. 7) and has basically the same configuration.Thus, in terminal apparatus 600 of the present embodiment, the differentcomponents from terminal apparatus 500 (refer to FIG. 7) will bedescribed, and other same components are assigned the same referencenumerals and will not be described.

In terminal apparatus 600 shown in FIG. 9, transmission rate requestgenerating sections 144 and 154 output the quality estimation resultsrespectively corresponding to the antennas of the communicating party(including the transmission rate request signal of each antenna) tocomparing section 563 and transmission controlling section 620.Furthermore, the channel quality estimation method performed bytransmission rate request generating sections 144 and 154 is the same asmethods described in Embodiments 1 and 4, and description thereof willbe omitted.

Comparing section 563 calculates the difference between the qualityestimation results (to be more specific, transmission rate signals ofthe transmitting antennas) inputted from transmission rate requestgenerating sections 144 and 154, compares the difference between thetransmission rate request signal values of the antennas on thetransmitting side with a threshold value and outputs the result totransmission controlling section 620. Here, the comparison resultcalculated by comparing section 563 includes information indicating fromwhich transmitting antenna the communicating party that transmits datato terminal apparatus 100 performs transmission.

Transmission controlling section 620 controls transmission of thetransmission signal transmitted to the communicating party (transmittingapparatus 200), and, similar to transmission controlling section 120(refer to FIG. 2), stores and outputs the transmission signal tomodulating and encoding section 125 at the transmission time.

Further, based on information which is inputted from comparing section563 and indicates from which transmitting antenna the base station,which is the communicating party, performs transmission, transmissioncontrolling section 620 controls transmission by transmittinginformation indicating corresponding to how many antennas thetransmission rate request signals are transmitted to the base station inaddition to the transmission rate request signal.

Further, the configuration of the base station that receives a signalfrom terminal apparatus 600 differs only in the operation of eachsection of transmitting apparatus 200 shown in FIG. 3, and has basicallythe same configuration. Thus, the configuration of the base station ofEmbodiment 5 will be described with reference to FIG. 3.

In the base station (here, transmitting apparatus 200 shown in FIG. 3),which is a communicating party of terminal apparatus 600, S/P convertingsection 249 extracts transmission rate request signals based oninformation which is reported by terminal apparatus 600 and indicatescorresponding to how many antennas the transmission rate request signalsare transmitted, and outputs the extraction result to transmissioncontrolling section 260.

According to terminal apparatus 600 having such a configuration, bytransmitting information indicating the transmitting antenna of the basestation to the base station, which is the communicating party (forexample, transmitting apparatus 200 shown in FIG. 3), it is possible toset the transmitting antenna and transmission rate of the transmittingantenna and transmit data at the base station, based on the transmissionrate request value having the best channel quality and informationindicating corresponding to how many transmitting antennas thetransmission rate request signals are transmitted to the base station.

As a result, even during high-speed movement of terminal apparatus 600where the channel state upon report of the previous transmission raterequest value substantially differs from the channel state upontransmission, the base station (the communicating party of terminalapparatus 600) side can transmit data using transmitting antennascorresponding to the number of transmitting antennas requested byterminal apparatus 600. It is thereby possible to prevent a decrease inthe throughput.

Furthermore, when the number of transmitting antennas is two,information indicating from which antenna the base station performstransmission may be one bit, which is sufficiently small compared to atransmission rate request signal (for example, the transmission raterequest signal in 3GPP requires 5 bits), so that the amount of controlinformation in uplink does not substantially increase.

Further, although the case has been described in Embodiment 5 where thecommunicating party of terminal apparatus 600, for example, a basestation that performs MIMO transmission, performs transmission only fromone transmitting antenna, the present invention is not limited to this,and same information may be transmitted from a plurality of transmittingantennas. In this case, it is not necessary to report informationindicating which transmitting antenna has good channel quality to thecommunicating party. However, it is preferable to perform transmissiononly from one transmitting antenna so as to reduce transmission power atthe base station.

The communication apparatus according to Embodiment 1 of the presentinvention that transmits transmission data and transmission rate requestsignals corresponding to a plurality of transmitting antennas to acommunicating party of a MIMO communication scheme that transmitsdifferent data from the plurality of transmitting antennas byindependently setting a transmission rate per transmitting antennaemploys a configuration including: a transmitting section that transmitsthe transmission data and the transmission rate request signals; and acontrolling section that controls transmission of signals to betransmitted from the transmitting section, wherein the controllingsection transmits, through the transmitting section, the transmissionrate request signals corresponding to less transmitting antennas thanthe plurality of transmitting antennas, based on a comparison resultbetween a difference between the transmission rate request signals ofthe transmitting antennas of the communicating party and a predeterminedvalue.

According to this configuration, transmission rate request signalscorresponding to less antennas than a plurality of antennas aretransmitted based on a comparison result with a predetermined value to acommunicating party of a MIMO communication scheme that transmitsdifferent data from the plurality of transmitting antennas byindependently setting a transmission rate per transmitting antenna, sothat transmission rate request signals transmitted to the communicatingparty do not become equivalent times of the number of transmittingantennas of the communicating party. Thus, it is possible to performtransmission by reducing transmission rate request signals withoutsubstantially decreasing transmission efficiency, so that it is possibleto reduce interference to other receivers (users) and reduce powerconsumption upon transmission of rate request signals.

The communication apparatus according to Embodiment 2 of the presentinvention employs a configuration wherein the controlling sectioncompares the difference between the transmission rate request signals ofthe transmitting antennas of the communicating party with thepredetermined value, and, when the difference is smaller than thepredetermined value, transmits the transmission rate request signalscorresponding to less transmitting antennas than the plurality oftransmitting antennas.

According to this configuration, it is possible to reduce transmissionrate request signals without substantially decreasing transmissionefficiency upon transmission of the transmission rate request signals,and reduce interference and power consumption.

The communication apparatus according to Embodiment 3 of the presentinvention employs a configuration wherein the controlling sectioncompares the difference between the transmission rate request signals ofthe transmitting antennas of the communicating party with thepredetermined value, and, when the difference is larger than thepredetermined value, transmits the transmission rate request signalscorresponding to less transmitting antennas than the plurality oftransmitting antennas.

According to this configuration, it is possible to reduce transmissionrate request signals without substantially decreasing transmissionefficiency upon transmission of the transmission rate request signals,and reduce interference and power consumption.

The communication apparatus according to Embodiment 4 of the presentinvention employs a configuration wherein the controlling sectiontransmits the transmission rate request signal corresponding to onetransmitting antenna out of the plurality of transmitting antennas,based on a comparison result between the difference between thetransmission rate request signals of the transmitting antennas of thecommunicating party and the predetermined value.

According to this configuration, the transmission rate request signalcorresponding to one transmitting antenna out of the plurality oftransmitting antennas is transmitted to a communicating party thattransmits transmission rate request signals, so that it is possible atthe communicating party to reduce the amount of the throughput uponreception of the transmission rate request signal compared to a casewhere the transmission rate request signals corresponding to alltransmitting antennas are received, and reduce power consumption upontransmission of the transmission rate request signal compared to a casewhere the transmission rate request signals corresponding to alltransmitting antennas are transmitted.

The communication apparatus according to Embodiment 5 of the presentinvention employs a configuration wherein the controlling sectioncompares the difference between the transmission rate request signals ofthe transmitting antennas of the communicating party with thepredetermined value, and, when the difference is smaller than thepredetermined value, transmits only the transmission rate request signalhaving the smallest transmission rate request value out of thetransmission rate request values at the plurality of transmittingantennas.

According to this configuration, it is possible at the communicatingparty to set the transmission rate of the transmitting antenna basedonly on the smallest transmission rate request signal of eachtransmitting antenna, so that it is only necessary to extract thesmallest transmission rate request signal of each transmitting antennafrom the transmitted signal and it is possible to prevent deteriorationof the error rate upon extraction.

The communication apparatus according to Embodiment 6 of the presentinvention employs a configuration wherein the controlling sectiontransmits, to the communicating party, information indicating whetherthe transmission rate request signals are transmitted corresponding tothe number of transmitting antennas of the communicating party orcorresponding to only one transmitting antenna of the communicatingparty.

According to this configuration, in received data, the communicatingparty can perform detection upon extraction of transmission rate requestsignals based on information indicating whether the transmission raterequest signals are transmitted corresponding to the number oftransmitting antennas of the communicating party or corresponding toonly one transmitting antenna of the communicating party, so that it ispossible to further reduce false detection of transmission rate requestsignals by the communicating party compared to the embodiment having theabove configuration.

The communication apparatus of Embodiment 7 of the present inventionemploys a configuration wherein the predetermined value is variable.

According to this configuration, when transmission rate request signalsare transmitted, it is possible to further reduce interference to othercommunication apparatuses (users) compared to a case where acommunication apparatus of the above configuration is used.

The communication apparatus according to Embodiment 8 of the presentinvention employs a configuration wherein the controlling sectiontransmits only the transmission rate request signal having the largesttransmission rate request value when the difference between thetransmission rate request signals of the transmitting antennas of thecommunicating party is larger than the predetermined value.

According to this configuration, the communicating party can furtherprevent error rate deterioration compared to a case where thecommunicating party receives transmission rate request signals from acommunication apparatus having the above configuration.

The communication apparatus according to Embodiment 9 of the presentinvention employs a configuration wherein the controlling sectiontransmits to the communicating party information indicating atransmitting antenna at which a transmission rate is set correspondingto the transmission rate request signals to be transmitted to thecommunicating party.

According to this configuration, based on information indicating thetransmitting antenna at which a transmission rate corresponding totransmission rate request signals is set, the communicating partyperforms transmission after setting a transmission rate at predeterminedantennas, so that it is possible to transmit data from a plurality oftransmitting antennas at the transmission rate desired by thecommunication apparatus and further prevent a decrease in the throughputduring high-speed movement compared to the communication apparatus ofthe above configuration.

The communication method according to Embodiment 10 of the presentinvention of transmitting transmission data and transmission raterequest signals corresponding to a plurality of transmitting antennas toa communicating party that transmits different data from the pluralityof transmitting antennas by independently setting a transmission rateper transmitting antenna includes: a transmission step of transmittingthe transmission data and the transmission rate request signals; and acontrol step of controlling transmission of signals to be transmittedfrom the transmission step, wherein, the control step transmits thetransmission rate request signals corresponding to less transmittingantennas than the plurality of transmitting antennas, based on acomparison result between a difference between the transmission raterequest signals of the transmitting antennas of the communicating partyand a predetermined value.

According to this configuration, when the transmission rate requestsignals are transmitted to the communicating party employing a MIMOcommunication scheme, it is not necessary to transmit the transmissionrate request signals corresponding to all transmitting antennas of thecommunicating party, so that it is possible to reduce the transmissionrate request signals without substantially decreasing transmissionefficiency and reduce interference and power consumption.

The present application is based on Japanese Patent Application No.2005-21681, filed on Jan. 28, 2005, the entire content of which isexpressly incorporated by reference herein.

INDUSTRIAL APPLICABILITY

The communication apparatus and communication method of the presentinvention can reduce transmission rate request signals and performtransmission without substantially reducing transmission efficiency,have the effect of reducing interference and power consumption upontransmission of transmission rate request signals and are useful fortransmitting data in a MIMO communication scheme.

1. A communication apparatus that communicates with a communicating party of a multi-input multi-output (MIMO) communication scheme that transmits data from a plurality of transmitting antennas, the communication apparatus comprising: a transmitting section that transmits at least one of a plurality of transmission rate request values corresponding to the plurality of transmitting antennas; and a controlling section that controls transmission of the at least one transmission rate request value from the transmitting section, wherein: the controlling section controls the transmission of the at least one transmission rate request value based on a comparison result between a difference between the transmission rate request values and a predetermined value; when the difference between the transmission rate request values is smaller than the predetermined value, only a transmission rate request value having a smallest value out of the plurality of transmission rate request values is transmitted; when the difference between the transmission rate request values is equal to or larger than the predetermined value, all of the plurality of transmission rate request values are transmitted; and the transmitting section transmits, to the communicating party, information indicating whether only the transmission rate request value having the smallest value and corresponding to one of the plurality of transmitting antennas is transmitted or all of the plurality of transmission rate request values corresponding to the plurality of transmitting antennas are transmitted.
 2. The communication apparatus according to claim 1, wherein the predetermined value is variable.
 3. The communication apparatus according to claim 1, wherein the transmitting section transmits, to the communicating party, information indicating a transmitting antenna at which a transmission rate is set corresponding to the at least one transmission rate request value to be transmitted to the communicating party.
 4. A communication method for communicating with a communicating party that transmits data from a plurality of transmitting antennas, the communication method comprising: transmitting at least one of a plurality of transmission rate request values corresponding to the plurality of transmitting antennas; and controlling the transmitting of the at least one transmission rate request value, wherein: the transmitting of the at least one transmission rate request value is controlled based on a comparison result between a difference between the transmission rate request values and a predetermined value; when the difference between the transmission rate request values is smaller than the predetermined value, only a transmission rate request value having a smallest value out of the plurality of transmission rate request values is transmitted; when the difference between the transmission rate request values is equal to or larger than the predetermined value, all of the plurality of transmission rate request values are transmitted; and the communication method further comprises transmitting, to the communicating party, information indicating whether only the transmission rate request value having the smallest value and corresponding to one of the plurality of transmitting antennas is transmitted or all of the plurality of transmission rate request values corresponding to the plurality of transmitting antennas are transmitted. 